1. Field of the Invention
The present invention relates to a method for hydrocracking heavy fraction oils, particularly those containing at least 1.0 wt. % of asphaltene, that is, pentane-insoluble ingredients, using a hydrogen donating solvent.
2. Description of the Prior Art
The hydrogenolysis of heavy fraction oils has recently been used to a greater extent. Thus, there have been proposed many methods for thermalcracking, catalytic cracking, hydrogenolysis, etc.
The heavy fraction oils used herein are hydrocarbon oils containing at least 50 wt. % of a fraction boiling at 350.degree. C. or higher, particularly heavy fraction oils containing at least 1.0 wt. % of pentane-insoluble ingredients, and they include residual oils obtained by the atmospheric or reduced pressure distillation of crude oils, and oils obtained from coal, oil shale, oil sand, bitumen, superheavy crude oils and the like. The term "cracking" used herein is intended to indicate processes which give light fraction oils including naphtha, gasoline, kerosene and gas oil fractions by hydrocracking the heavy fraction oils.
The most serious and troublesome problems raised by the cracking of heavy fraction oils are, in general, the formation of carbonaceous materials and the clogging of various parts of an apparatus for the cracking with the carbonaceous materials. Further, the serious problem caused by the catalytic cracking of the heavy fraction oils is a decrease in catalytic activity of the catalyst used. Still further, the cracking of the heavy fraction oils raises a problem as to an increase in amount of hydrogen consumed. These problems are rendered more serious as the heavier are the fraction oils to be cracked.
One of methods for solving these problems is a method comprising the use of a hydrogen donating solvent (For example, U.S. Pat. No. 4,430,197). It is well known that compounds obtained by hydrogenating polycyclic aromatic compounds, for instance, Tetralin (tetrahydronaphthalene), serve as a hydrogen donor and that catalysts are not necessarily required for the hydrogenolysis of heavy fraction oils with the use of such a hydrogen donating solvent, and this reaction proceeds under a comparatively low hydrogen pressure (For example, U.S. Pat. No. 4,294,686 and Oil & Gas Journal, Nov. 22, 1982, pp. 111-116). The above method so known have very often been attempted to be used industrially (For example, U.S. Pat. No. 2,953,513). It is also known that such hydrogen donating substances are contained in thermocracked oils, catalytically cracked oils, hydrocracked oils and the like and function, per se, as an effective hydrogen donating solvent (For example, U.S. Pat. No. 3,970,545).
In these known methods, since the cracking reaction takes place effectively only at comparatively high temperatures, the carbonaceous substances or precursors thereof are produced at the time of the cracking and clog the various parts an apparatus for the cracking thereby hindering the long-term safe operation of the apparatus, this being the most serious problem.
Further, Japanese Pat. Appln. Laid-Open Gazette No. 61-235492 which corresponds to U.S. Pat. No. 4,640,765 discloses that partitions made from a solid catalyst are provided in a reaction tower to generate natural circulation of a liquid thereby obtaining the necessary liquid flow velocity to avoid clogging and the like with carbonaceous substances and that not only cracking reactions are caused to be effectively carried out, but also the formation of the carbonaceous substances is greatly reduced owing to the presence or use of a catalyst capable of hydrogenation in the reaction tower.
The above techniques so disclosed enable the formation of carbonaceous substances and precursors thereof to be greatly inhibited, but they still permit small amounts of the carbonaceous substances and precursor thereof to be produced thereby raising problems as to clogging in the devices and piping used downstream of the reaction tower.